Why did some grasslands expand during the ice ages?

During the ice ages of the Pleistocene Epoch, grasslands and savannas expanded significantly in many temperate regions, often at the expense of forests.1

This expansion was primarily driven by the long, cool, and dry climatic conditions that characterized these glacial intervals. Several factors contributed to this shift:1

• Reduced Moisture: Global cooling led to lower ocean surface temperatures, which reduced evaporation and slowed the hydrologic cycle. This resulted in less cloud formation and precipitation, creating environments that were too dry to support dense forest cover.1
• Climatic Stress: Forests, particularly in tropical and temperate areas, require adequate moisture to thrive. As conditions became more arid, these areas were replaced by vegetation better adapted to drier, cooler environments, such as grasslands.21
• Feedback Loops: The replacement of forests by other vegetation types, such as tundra or grassland, altered the Earth's albedo and reduced the amount of water vapor and latent heat released into the atmosphere through transpiration, which reinforced the cooling trend.3

In some regions, these grasslands reached an extent approaching their modern distribution specifically during these cold, dry intervals.2